Agronomic effectiveness of Chatham Rise sediments

Abstract

Sediments from the Chatham Rise, a by-product from phosphate nodule extraction, could have some agronomic value for New Zealand pastoral soils. Two pot trials were carried out to investigate the agronomic effectiveness of four selected sediments with varying levels of nutrients, mainly calcium (Ca) and phosphorus (P). The first experiment tested all sediments at a range of application rates in contrasting soils growing Italian ryegrass (Lolium multiflorum). The second experiment tested one selected sediment at a constant rate of P against Chatham Rise phosphate rock (PR) and triple superphosphate (TSP), growing monocultures of Italian ryegrass and white clover (Trifolium repens). Results showed that sediment application did not increase ryegrass dry matter yield or P uptake, however did have a liming effect. One sediment, DD44W, actually reduced clover dry matter yield in the second experiment, and P uptake was significantly reduced compared to PR and TSP. The findings demonstrate that these sediments are of limited value as a P fertiliser, however the sediments with higher Ca content can be a useful liming material. The implications are that if the mining project gets consent, these sediments could be retained rather than returned to the sea floor after phosphate nodule extraction. These findings could also be beneficial in the consenting process and could provide a useful product for New Zealand farmers while also providing a solution that reduces the environmental impacts of the sea floor mining operation.... [Show full abstract]